1. Technical Field
This invention relates generally to communication systems and, more particularly, to Radio Frequency (RF) signal amplification within wireless devices operating in wireless communication systems.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wired communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), wireless application protocol (WAP), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel of the other parties (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and exchange information over that channel. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wire lined or wireless network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.) to participate in wireless communications. As is known, the receiver receives RF signals, removes the RF carrier frequency from the RF signals via one or more intermediate frequency stages, and demodulates the signals in accordance with a particular wireless communication standard to recapture the transmitted data. The transmitter converts data into RF signals by modulating the data in accordance with the particular wireless communication standard and adds an RF carrier to the modulated data in one or more intermediate frequency stages to produce the RF signals.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier (LNA), zero or more intermediate frequency (IF) stages, a filtering stage, and a data recovery stage in many designs. The low noise amplifier receives an inbound RF signal via the antenna and amplifies it. The down converters mix the amplified RF signal with one or more local oscillations to convert the amplified RF signal into a baseband signal or an intermediate frequency signal. As used herein, the term “low IF” refers to both baseband and low intermediate frequency signals. A filtering stage filters the low IF signals to attenuate unwanted out of band signals to produce a filtered signal. The data recovery stage recovers raw data from the filtered signal in accordance with the particular wireless communication standard.
There is a need today for a wireless transceiver system that allows for full integration of circuit designs that support high data rate and wideband communications. Stated differently, there is a need for wireless transceiver systems formed on an integrated circuit that have the capability to convert between baseband and a specified RF band in a single step to avoid the image rejection problems that are commonly known for IF approach. Thus, it is desirable to design direct conversion radio transceivers to allow a transceiver to be built on one integrated circuit without any image problem.
As the demand for enhanced performance (e.g., reduced interference and/or noise, improved quality of service, compliance with multiple standards, increased broadband applications, etc.), smaller sizes, lower power consumption, and reduced cost, wireless communication device engineers are faced with a very difficult design challenge to develop such a wireless communication device.
To minimize the size and number of discrete circuits within a device, there is a desire to incorporate power amplifiers into a single device on a radio transceiver integrated circuit or device. One problem with integrating radio transceiver circuits with power amplifiers, however, is that the power amplifiers generate significant temperatures that affect device reliability and/or operation. An additional need exists, therefore, for an integrated power amplifier within a transceiver device that addresses the various problems related to increased temperatures generated by the power amplifier of an integrated circuit or device. It is desired to monitor the temperature of the PA and to control the power level to prevent being overheated and reducing its reliability.
More generally, a temperature sensor is a common feature of complex mixed-signal integrated circuits. It is used to compensate for the sensitivity to temperature of integrated circuits such as but not limited to RF amplifiers and active filters. A particularly challenging problem of a temperature sensor is generating an output that is accurate in absolute terms from part to part such that no calibration of the sensor itself is required. Typically the absolute accuracy of a sensor is limited by the stability of process parameters and by circuit imperfections such as amplifier input offset originating from device mismatch.